JP2008268727A - Color decomposition/composition optical system and image projection apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simplify a configuration of a color decomposition/composition system by reducing the number of optical components including multilayer films, for use in the color resolving and synthesizing system. <P>SOLUTION: The color decomposition/composition optical system includes a first polarization separating surface for polarizing and separating green light and a second polarization separating surface for polarizing and separating red light and blue light. The first polarization separating surface guides illumination light in green to a liquid crystal display device for green and guides light reflected by the liquid crystal display device for green to a direction different from that of the illumination light. The second polarization separating surface resolves illumination light in red and illumination light in blue to guide them to a liquid crystal display device for red and a liquid crystal display device for blue respectively and combines image light reflected by the liquid crystal display device for red and image light reflected by the liquid crystal display device for blue to guide combined light to the first polarization separating surface. The first polarization separating surface combines image light of green light, red light, and blue light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color separation / synthesis optical system, and more particularly to a color separation / synthesis optical system used in an image projection apparatus such as a liquid crystal projector and the image projection apparatus.

  Conventionally, a color separation / synthesis optical system used in a reflective liquid crystal projector or the like is arranged in a light path between an illumination optical system and a projection optical system, as in Patent Document 1, with a dichroic mirror and three polarization beam splitters (PBS). Was. However, this configuration has a large number of parts, and further miniaturization has been demanded.

Therefore, as in Patent Document 2, an example in which a liquid crystal projector is configured using one PBS and one dichroic prism has been proposed, and miniaturization of the liquid crystal projector has been achieved.
JP 2001-154152 A JP 2003-021807 A

  However, in the configuration as in Patent Document 2, the image light reflected from the liquid crystal panel passes through the dichroic prism before being analyzed by the PBS. Therefore, the polarization state immediately after being reflected from the liquid crystal panel is changed by passing through the dichroic prism, and the contrast is lowered.

  Therefore, an object of the present invention is to provide a color separation / synthesis optical system and an image projection apparatus that can output image light with a small number of parts and high contrast.

  The color separation / synthesis optical system of the present invention includes a first polarization separation surface having polarization separation characteristics for light in the first wavelength region, and a second polarization separation characteristic for light in the second and third wavelength regions. A color separation / synthesis optical system comprising a polarization separation surface, wherein the first polarization separation surface guides illumination light in the first wavelength region to a first liquid crystal display element and is reflected by the first liquid crystal display element. The image light is guided in a direction different from that of the illumination light, and the second polarization separation surface decomposes the illumination light in the second wavelength region and the illumination light in the third wavelength region, respectively, while separating each of the second liquid crystals. In addition to guiding to the display element and the third liquid crystal display element, the image light reflected by the second liquid crystal display element and the image light reflected by the third liquid crystal display element are combined and guided to the first polarization separation surface. Reflected by the first liquid crystal display element by the first polarization separation surface. And the image light, is characterized by combining the reflected image light in the second polarization splitting surface in the synthesized second and third liquid crystal display device.

The image projection apparatus of the present invention includes first, second, and third liquid crystal display elements, a projection optical system that projects image light from the first, second, and third liquid crystal display elements, and light from a light source for the first, An image projection apparatus including a color separation / synthesis optical system that guides image light from the first, second, and third liquid crystal display elements to the projection optical system while guiding the light to the second and third liquid crystal display elements. The optical system has a first polarization separation surface having polarization separation characteristics for light in the first wavelength region and a second polarization separation surface having polarization separation properties for light in the second and third wavelength regions. The first polarization separation surface guides the illumination light in the first wavelength region to the first liquid crystal display element and guides the image light reflected by the first liquid crystal display element to the projection optical system. And the second polarization separation surface is adapted to transmit the illumination light in the second wavelength region and the illumination light in the third wavelength region. Each of them is guided to the second liquid crystal display element and the third liquid crystal display element, and the image light reflected by the second liquid crystal display element and the image light reflected by the third liquid crystal display element are synthesized. Leading to the first polarization separation surface;
The first polarization separation surface combines the image light reflected by the first liquid crystal display element and the image light reflected by the second and third liquid crystal display elements synthesized by the second polarization separation surface. Then, it is guided to the projection optical system.

  According to the present invention, there are provided a color separation / synthesis optical system capable of outputting image light with a small number of components and high contrast, and an image projection apparatus capable of projecting a high contrast image using the same. It becomes possible.

  Embodiments of the color separation / synthesis optical system of the present invention and an image projection apparatus having the same will be described in detail below. In the following first, second, third, and fourth embodiments, the entire image projection apparatus is described, but the present invention is one of the configurations of the color separation / synthesis optical system 200 in the image projection apparatus. It is completed with the composition of the department. Specifically, as can be seen from Example 4 to be described later, dichroic mirrors 6, 26, 46 and mirrors 7, 27 described in Examples 1 to 3 of the color separation / synthesis optical system 200. , 47 and the like are not particularly included as constituent elements, and the present invention is completed.

  Specifically, the color separation / synthesis optical system of the present embodiment includes a first polarization separation surface having polarization separation characteristics (polarization separation function) for light in the first wavelength region, light in the second wavelength region, And a second polarization separation surface having polarization separation characteristics (polarization separation function) for light in the three wavelength regions. Here, the first polarization separation surface guides the illumination light in the first wavelength region to the first liquid crystal display element, and guides the image light reflected by the first liquid crystal display element in a direction different from the illumination light. Next, the second polarization splitting surface guides the illumination light in the second wavelength region and the illumination light in the third wavelength region to the second liquid crystal display element and the third liquid crystal display element, respectively. Further, the second polarization separation surface combines the image light reflected by the second liquid crystal display element and the image light reflected by the third liquid crystal display element and guides it to the first polarization separation surface. Finally, the image light reflected by the first liquid crystal display element by the first polarization separation surface, the image light reflected by the second liquid crystal display element and the third liquid crystal display element synthesized by the second polarization separation surface, and Is synthesized.

  In the present embodiment, the polarization separation characteristic (polarization separation function) is a characteristic (function) that reflects one of lights having different polarization directions and transmits the other. With reflection (transmission), it is desirable to reflect (transmit) 100% of incident light, but it is desirable to reflect (transmit) at least 50% (preferably 75% or more) of components.

  In the following embodiments, the first wavelength region light will be described as green light, the second wavelength region light as blue light, and the third wavelength region light as red light. Any color light may be applied.

  With such a configuration, a color separation / synthesis optical system capable of outputting image light with a small number of components and high contrast, and an image projection apparatus capable of projecting a high contrast image using the same. Can be provided.

(First embodiment)
A first embodiment of the present invention will be described with reference to FIGS.

  The outline of the first embodiment will be described with reference to FIG. In the first embodiment, white light from the light source 1 is guided to the reflective liquid crystal display elements (image display elements) 10R, G, and B using the illumination optical system 100. Then, the image light emitted from the reflective liquid crystal display elements 10R, 10G, 10B (first, second, and third liquid crystal display elements) is screened using a projection optical system (projection lens, but not limited to a lens) 16. And so on. Here, between the illumination optical system 100 and the projection optical system 16, there is disposed a color separation / synthesis optical system 200 that color-separates illumination light that has passed through the illumination optical system and guides it to each of the reflective liquid crystal display elements 10R, 10G, and 10B. Has been. The color separation / synthesis optical system 200 also has a function of synthesizing image light emitted from each of the reflective liquid crystal display elements 10R, 10G, and 10B and guiding it to the projection optical system 16. In this embodiment, the color separation / synthesis optical system 200 will be described in detail below.

  First, the illumination optical system 100 will be described with reference to FIG. In FIG. 1, reference numeral 100 surrounded by a broken line represents the illumination optical system as described above, and reference numeral 200 also surrounded by the broken line represents a color separation / synthesis optical system. 1 is incident on the center of the three reflective liquid crystal display elements 10R, 10G, 10B, and exits from the center of the reflective liquid crystal display elements 10R, 10G, 10B, and is projected onto the screen. The optical axis of the optical system led from the light source to the screen is shown.

  A light beam emitted in all directions from a light source (lamp light emitting portion) 1 that emits white light is emitted as substantially parallel light by a parabolic reflector 2. The parallel luminous flux is divided into a plurality of partial luminous fluxes by the first lens array 3, and each partial luminous flux is condensed near the second lens array 4 by the first lens array 3, and the plurality of partial luminous fluxes are collected. Each light beam forms a light source image (secondary light source image). The split luminous flux emitted from the second lens array 4 is collected by the condenser lens 5 and illuminates the reflective liquid crystal panels 10R, G, and B in a superimposed manner. An infrared cut filter (not shown) or the like may be arranged on the light source side of the first lens array 3.

  Here, immediately after the second lens array 4 (on the light source side of the condenser lens 5), a polarization conversion element (not shown) is arranged, and the polarization conversion element receives each of the plurality of partial light beams described above. It converts into linearly polarized light (here P-polarized light) having the same polarization direction. In this polarization conversion element, a plurality of polarization conversion elements are arranged in an array (in a direction crossing the optical axis of the illumination optical system 100 or in a direction in which a plurality of lenses in the first and second lens arrays are arranged). They are arranged and convert non-polarized light into linearly polarized light (P-polarized light). Therefore, this polarization conversion element (not shown) may be referred to as a polarization conversion element array.

  A light beam (illumination light) emitted from the illumination optical system 100 configured as described above is guided to the color separation / synthesis optical system 200.

  Next, the color separation / synthesis optical system 200 will be mainly described with reference to FIGS.

  The dichroic mirror 6 reflects blue light (second wavelength region light, second color light, B) and red light (third wavelength region light, third color light, R) of white light from the light source. , Green light (light in the first wavelength region, first color light, G) is transmitted. Blue light is light in the wavelength region of about 400 nm to 500 nm, green light is light in the wavelength region of about 500 nm to 600 nm, and red light is light in the wavelength region of about 600 nm to 700 nm. pointing. That is, each color light should just point out the light of a mutually different wavelength range.

  The optical path of green light that has passed through the dichroic mirror 6 will be described.

  A mirror 7 reflects the green light transmitted through the dichroic mirror 6. 8 is an incident side (light source side) polarized light that transmits only P-polarized light (desired polarization direction) and absorbs or reflects S-polarized light (polarization direction orthogonal to the desired polarization direction). A plate (incident side polarizing plate for green light, first incident side polarizing plate). 9 has a polarization separation surface (first polarization separation surface) that transmits P-polarized light (first linearly polarized light) and reflects S-polarized light (second linearly polarized light) whose polarization direction is orthogonal to the P-polarized light. This is a polarizing beam splitter. The polarization separation surface can be said to be a surface on which a polarization separation film is applied or a surface on which two prisms are bonded.

  10G is a reflective liquid crystal display element for green (for green light) that reflects incident light and modulates the image, 11G is a 1/4 wavelength plate for green, and 70 is an optical path adjustment for adjusting the optical path length. It is a prism. The optical path length adjusting prism 70 has substantially the same optical path length from the reflective liquid crystal display element to the screen (projection surface) for each color light (the shortest optical path length is 90% or more, preferably 97% or more of the longest optical path length). ). The P-polarized green light (illumination light) that has passed through the first polarizing beam splitter described above enters the reflective liquid crystal display element for green light via the optical path adjusting prism 70 and the quarter wavelength plate 11G. The green light incident on the reflective liquid crystal display element is image-modulated (for example, partly modulated to S-polarized light) and reflected, and again passes through the optical path adjusting prism 70 and the quarter-wave plate 11G to be the first polarized beam. It enters the splitter. Of the green light incident on the first polarization beam splitter, S-polarized light (image light) is reflected by the polarization separation surface and guided to the projection optical system 16. In this way, green image light is projected onto the projection surface. Here, the light guided to the projection optical system at the latter stage and projected onto the projection surface, that is, the polarization direction can be changed from P-polarized light to S-polarized light (or from S-polarized light to P-polarized light) by the reflective liquid crystal display element. This light is referred to as image light. Similarly, for red light and blue light, which will be described later, light (with a polarization direction) guided to the projection optical system is referred to as image light.

  The optical paths of blue light and red light reflected by the dichroic mirror 6 will be described.

  12 is an incident side (light source side) polarizing plate that transmits P-polarized light of red light and blue light and absorbs or reflects S-polarized light (incident side polarizing plate for red light and blue light, or polarized light for white light). Plate, second incident-side polarizing plate). The red light and blue light that have passed through the incident-side polarizing plate 12 are incident on the second polarizing beam splitter 13 as P-polarized light.

  The second polarization beam splitter 13 is a polarization beam splitter having wavelength characteristics (polarization separation characteristics, polarization separation function) as shown in FIG. That is, a polarized light separation surface (a surface on which a polarization separation film is applied or a surface where two prisms face each other, a second polarization separation having a characteristic that the polarization separation characteristics are reversed with respect to red light and blue light. Surface). Specifically, a polarization separation surface (second polarization separation surface) having characteristics of transmitting S-polarized light and reflecting P-polarized light for blue light, and reflecting S-polarized light and transmitting P-polarized light for red light. A polarizing beam splitter.

  Therefore, the P-polarized blue light incident on the second polarizing beam splitter is reflected and enters the blue (blue light) reflective liquid crystal display element 10B via the quarter-wave plate 11B. The blue light modulated and reflected by the blue reflective liquid crystal display element 10B is incident on the second polarizing beam splitter again via the quarter-wave plate 11B. Of the blue light incident on the second polarizing beam splitter, blue light (image light) modulated into S-polarized light in the liquid crystal display element 10B passes through the second polarizing beam splitter and travels in the direction of the projection optical system. Led.

  Also, the P-polarized red light incident on the second polarizing beam splitter is transmitted and enters the red (red light) reflective liquid crystal display element 10R via the quarter-wave plate 11R. The red light (image light) modulated and reflected by the red reflective liquid crystal display element 10R is incident on the second polarizing beam splitter again via the quarter-wave plate 11R. Of the red light incident on the second polarizing beam splitter, the red light modulated into S-polarized light in the liquid crystal display element 10R is reflected by the second polarizing beam splitter and guided toward the projection optical system 16.

  In this way, the S-polarized red light and blue light guided from the second polarizing beam splitter toward the projection optical system 16 transmit the S-polarized light and absorb or reflect the P-polarized light. Is incident on. The S-polarized light emitted from the output-side polarizing plate 14 enters the half-wave plate 15 and is converted into P-polarized light. The P-polarized red light and blue light emitted from the half-wave plate 15 pass through the first polarizing beam splitter described above, enter the projection optical system 16, and are projected onto the projection surface.

  In the case of black display, all the light reflected from the green reflective liquid crystal display element is incident on the first polarizing beam splitter again as P-polarized light, and the first polarizing beam splitter is used. Through the light source. Similarly, all red light reflected from the reflective liquid crystal display element for red is transmitted through the second polarizing beam splitter again as P-polarized light and returns to the light source direction. All the blue light reflected from the blue reflective liquid crystal display element is again reflected by the second polarizing beam splitter as P-polarized light and returned to the light source direction. Of course, light that does not become image light (light that is not modulated by the liquid crystal display element and whose polarization direction does not change) is returned to the light source direction in the same manner as the light in the black display.

  In the first embodiment, the optical path adjusting prism 70 is disposed between the first polarizing beam splitter 9 and the liquid crystal display element 10G (on the first liquid crystal display element side of the first polarizing beam splitter), but this is not restrictive. For example, as shown in FIG. 8, the optical path adjusting prism 70 may not be disposed, and a gap may be provided between the first polarizing beam splitter and the green reflective liquid crystal display element 10G (first embodiment). First modification of example). In this case, at least the distance between the first polarizing beam splitter and the green reflective liquid crystal display element 10G is set as the distance between the second polarizing beam splitter and the blue or red reflective liquid crystal display element. It is preferable to make it larger. More preferably, the projection optical system 16 (the optical surface closest to the reflective liquid crystal surface element among a plurality of optical surfaces (lens surfaces, etc.) of the projection optical system 16) and each reflective liquid crystal display element 10R, G, B are used. The interval (back focus in the optical path of each color light) may be made substantially the same. Thus, the optical path length from the projection optical system 16 to each of the reflective liquid crystal display elements 10R, G, B is substantially the same (the shortest optical path length is 90% or more of the longest optical path length, more preferably 97% or more. ), Only one color light will not be blurred or the magnification will not be different. Of course, as shown in FIG. 8, the optical path adjusting prism 70 is eliminated, and the reflective liquid crystal display element 10G and the first polarizing beam splitter 11G are within a range in which the image quality of the projected image is not deteriorated (within the allowable range even if it is deteriorated). You may narrow a space | interval with (projection optical system 16).

  Further, an optical element such as a lens is disposed between the first polarizing beam splitter 9 and the liquid crystal display elements 10R and 10B (on the second liquid crystal display element side and / or the third liquid crystal display element side of the first polarizing beam splitter). It doesn't matter. In this case, a common lens may be disposed in the red light optical path and the blue light optical path between the first polarizing beam splitter 9 and the second polarizing beam splitter 13. Further, different lenses are arranged between the red reflective liquid crystal display element 10R and the second polarizing beam splitter 13 and between the blue reflective liquid crystal display element 10B and the second polarizing beam splitter 13, respectively. You may do it.

  Further, the projection optical system may have chromatic aberration to compensate for the optical path length difference of the color light. At this time, it is desirable to give chromatic aberration in consideration of the fact that only the optical path of green light is shorter than the optical paths of other red light and blue light. The lens referred to here is of course an optical element having optical power (reciprocal of focal length, refractive power), and may be a diffractive optical element or the like. Further, instead of the lens mentioned here, an optical surface having optical power (refractive power) may be provided by providing a curvature to an existing optical element or providing a diffractive surface.

  If the distances (optical path lengths) from the light source 1 (or the second lens array on which the secondary light source image is formed) to the reflective liquid crystal display elements 10R, G, and B are different, three reflective liquid crystal display elements are used. The illuminance distribution above may not be the same. Specifically, in the first embodiment, the distance from the light source 1 to the reflective liquid crystal display element 10R for red and the reflective liquid crystal display element 10B for blue is the same, but the reflective liquid crystal display for green is used. Only the distance to the element 10G is increased. In such a case, the illuminance distribution of the reflective liquid crystal display element 10G for green is different from the illuminance distribution of the reflective liquid crystal display elements 10R and 10B for red and blue, and on either reflective liquid crystal display element. Even if the illuminance distribution is uniform, the other illuminance distribution may be non-uniform.

  Therefore, in order to make the illuminance distribution on the three reflective liquid crystal display elements the same (preferably all illuminance distribution is uniform), an optical element is placed on the optical path from the dichroic mirror 6 to the first polarizing beam splitter 9. It is good to arrange. The optical element may be an optical element having the power (condensing power, refractive power) of an optical element, such as a refractive lens or a diffractive optical element, and by such an optical element, three reflective liquid crystal display elements The upper illuminance distribution can be made the same. Specifically, a light source image (referred to as a tertiary light source) is formed between the dichroic mirror 6 and the first polarizing beam splitter 9, and a green reflective liquid crystal display element with a light beam from the tertiary light source. (Kohler lighting). As a result, the optical position of the three reflective liquid crystal display elements with respect to the light source can be made the same (substantially the same) by the added optical element, and all three reflective liquid crystal display elements can be illuminated equally uniformly. I can do it. The added optical element includes at least one positive lens disposed between the dichroic mirror 6 and the mirror 7 and at least one positive lens disposed between the mirror 7 and the incident-side polarizing plate 8. It is desirable to include.

  In addition, when each color light leaks and is projected onto the projection surface during the black display described above, the image on the projection surface appears to float white even if black display is performed. Therefore, even if each of the quarter-wave plates 11R, 11G, and 11B is adjusted so as to reduce the light amount of each color light leakage light (light projected on the projection surface during black display) during black display. good.

  In this embodiment, unpolarized light from the light source is converted to P-polarized light by a polarization conversion element (polarization conversion element array) (not shown), but of course, it may be converted to S-polarized light.

  In Embodiment 1, a polarization beam splitter having a polarization separation surface having polarization separation characteristics as shown in FIG. 2 is used as the second polarization beam splitter, but this is not restrictive. Specifically, a polarization beam splitter having a polarization separation surface having characteristics obtained by reversing the polarization separation characteristic for red light and the polarization separation characteristic for blue light may be used. In that case, if the positions of the reflective liquid crystal display element for red and the reflective liquid crystal display element for blue are reversed, the same effects as in the present embodiment can be obtained.

  The polarization separation surface (element) generally has substantially the same polarization separation characteristics (for example, characteristics that reflect S-polarized light and transmit P-polarized light) with respect to light in the entire visible light region. There are many things. The first polarization beam splitter 9 (first polarization separation surface) of the present embodiment is a general polarization beam splitter that reflects S-polarized light with respect to light in the entire visible light region. It has a polarization separation characteristic that transmits P-polarized light.

  However, the second polarizing beam splitter 24 of this embodiment is slightly different from the above-described polarizing beam splitter (first polarizing beam splitter). As shown in FIG. 2, the second polarizing beam splitter transmits S-polarized light and reflects P-polarized light for red light, and reflects S-polarized light and reflects P-polarized light for blue light. The polarization separation characteristic changes depending on the wavelength (color) in the visible light region. In this way, even if the polarization separation characteristic changes depending on the wavelength, the polarization separation characteristic (especially for any of red light, green light, and blue light) in the visible light region (reflects S-polarized light and reflects P-polarized light A surface (element) that transmits the light beam or vice versa is referred to as a polarization separation surface (element).

  A material having a polarization separation characteristic as shown in FIG. 6 described in detail in Example 3 is also referred to as a polarization separation surface (element). That is, for light in a certain wavelength region (blue light in FIG. 6), S-polarized light is transmitted and P-polarized light is reflected, and for light in another wavelength region (red light in FIG. 6), S-polarized light. A surface having polarization separation characteristics that transmits (or reflects) both light and P-polarized light is also referred to as a polarization separation surface. Here, reflecting means that at least 50% (preferably 75%) of incident light is reflected, and conversely, transmitting means at least 50% of incident light ( (Preferably 75%) More light may be transmitted.

  In the first embodiment and other embodiments described later, the color light is assumed to be red, green, and blue. However, the present invention is not limited to this, and four or more color lights may be used. The method of dividing the wavelength region may be different from the above-described method of dividing.

  The polarizing plate described here guides light in a predetermined polarization direction to the subsequent optical system, and blocks (absorbs) light in the polarization direction orthogonal to the predetermined polarization direction with respect to the subsequent optical system. Alternatively, it is an optical element that leads in a different direction from the optical system in the subsequent stage. Although all the polarizing plates used in Example 1 have been described as functioning as polarizing plates for white light, that is, all of red light, green light, and blue light, this is not restrictive. It is sufficient if it functions as a polarizing plate for light in a wavelength region corresponding to the color light incident on the polarizing plate.

  When the image projection apparatus is configured in this manner, the red light and the blue light are analyzed immediately after being emitted from the reflective liquid crystal display element, so that the contrast between the red light and the blue light is reduced even if the number of components is small. There is nothing. That is, it is possible to provide an image projection apparatus capable of projecting an image with a small number of parts and high contrast, and a color separation / synthesis optical system constituting the image projection apparatus.

  As described in the present Example 1 and Examples 2 and 3 below, when having an optical element (dichroic mirror 6 of Example 1) that decomposes white light into green light, red, and blue light, Contrast is preferred, but not limited. The optical paths of red light, green light, and blue light described in the first embodiment may be interchanged.

(Second embodiment)
A second embodiment of the present invention will be described with reference to FIG. Parts not specifically described are the same as those in the first embodiment.

  The light source 1, the reflector 2, the illumination optical system 100, and the polarization conversion element (polarization conversion element array) (not shown) are the same as those in the first embodiment. However, in this embodiment, non-polarized light from the light source is converted into S-polarized light by the polarization conversion element.

  The color separation / synthesis optical system 300 will be described with reference to FIG.

  The dichroic mirror 26 has a characteristic of reflecting the color light of the blue light (B) and the red light (R) among the white light from the light source and transmitting the color light of the green light (G).

  The optical path of green light that has passed through the dichroic mirror 26 will be described.

  A mirror 27 reflects the green light transmitted through the dichroic mirror 26. 28 is an incident-side polarizing plate (green light) that transmits only S-polarized light (desired polarization direction) and absorbs or reflects P-polarized light (polarization direction orthogonal to the desired polarization direction). Incident side polarizing plate, first incident side polarizing plate). Reference numeral 29 denotes a first polarization beam splitter having a polarization separation surface (a surface provided with a polarization separation film or a surface where two prisms face each other) that transmits P-polarized light and reflects S-polarized light.

  Reference numeral 30G denotes a reflective liquid crystal display element for green (for green light) that reflects incident light and modulates an image, 31G is a quarter wavelength plate for green, and 70 is an optical path as in the first embodiment. This is an adjustment prism. S-polarized green light reflected by the first polarizing beam splitter 29 enters the reflective liquid crystal display element 30G for green light through the quarter-wave plate 31G and the optical path adjusting prism 70. The green light incident on the reflective liquid crystal display element is image-modulated (for example, partly modulated to P-polarized light) and reflected, and again passes through the optical path adjusting prism 70 and the quarter-wave plate 31G to be the first polarized beam. The light enters the splitter 29. Of the green light incident on the first polarization beam splitter, S-polarized light is reflected by the polarization separation surface and guided in the light source direction, and P-polarized light (image light) is transmitted through the polarization separation surface and guided to the projection optical system 37. . In this way, green image light is projected onto the projection surface by the projection optical system 37.

  The optical paths of blue light and red light reflected by the dichroic mirror 26 will be described.

  Reference numeral 32 denotes a mirror that reflects red light and blue light (it may be an optical element having a polarization separation surface that reflects only S-polarized light and transmits P-polarized light). The red light and blue light reflected by the mirror 32 transmit S-polarized light and absorb or reflect P-polarized light among the red light and blue light (incident-side polarization for red light and blue light). Plate or white light polarizing plate, second incident side polarizing plate) 33. The red light and blue light that have passed through the incident-side polarizing plate 33 are incident on the second polarization beam splitter 34 as S-polarized light.

  Similar to the second polarizing beam splitter 13 shown in the first embodiment, the second polarizing beam splitter 34 has wavelength characteristics (polarization separation characteristics, polarization separation function) as shown in FIG. It has a characteristic that the polarization separation characteristic is reversed with respect to blue light.

  Accordingly, the blue light of the S-polarized light incident on the second polarizing beam splitter 34 passes through the second polarizing beam splitter (the polarization separation surface thereof) and passes through the quarter wavelength plate 31B (for blue light). ) Is incident on the reflective liquid crystal display element 30B. The blue light modulated and reflected by the blue reflective liquid crystal display element 30B is incident on the second polarizing beam splitter 34 again through the quarter-wave plate 31B. Of the blue light incident on the second polarizing beam splitter 34, the blue light modulated into P-polarized light in the liquid crystal display element 30B is reflected by the second polarizing beam splitter and guided toward the projection optical system 37. .

  The S-polarized red light incident on the second polarizing beam splitter is reflected and enters the red (red light) reflective liquid crystal display element 30R via the quarter-wave plate 31R. The red light modulated and reflected by the red reflective liquid crystal display element 30R is incident on the second polarizing beam splitter 34 again via the quarter-wave plate 31R. Of the red light incident on the second polarizing beam splitter 34, the red light modulated into P-polarized light in the liquid crystal display element 30R passes through the second polarizing beam splitter and is guided in the direction of the projection optical system 37. .

  Thus, the P-polarized red light and blue light guided from the second polarizing beam splitter toward the projection optical system 37 transmit the P-polarized light and absorb or reflect the S-polarized light. Transparent. The P-polarized light emitted from the output-side polarizing plate 35 is converted into S-polarized light by the half-wave plate 36 and is incident on the first polarizing beam splitter 29 described above. Since the first polarization beam splitter has a characteristic of reflecting S-polarized light and transmitting P-polarized light, both S-polarized red light and blue light are polarized on the polarization separation surface of the first polarization beam splitter. It is reflected and guided in the direction of the projection optical system 37. In this way, red light and blue light are projected onto the projection surface.

  In the case of black display, each color light is returned to the light source direction as in the first embodiment.

  Also in the second embodiment, a lens may be disposed between the first polarizing beam splitter and the green reflective liquid crystal display element 30G. Further, between the first polarizing beam splitter and the second polarizing beam splitter, between the second polarizing beam splitter and the red reflective liquid crystal display element, or between the second polarizing beam splitter and the blue reflective liquid crystal. A lens may be disposed between the display element and the display element.

  In this second embodiment, S-polarized green light is incident on the first polarizing beam splitter, and S-polarized green light is incident on the green reflective liquid crystal display element 30G. . During black display, green light is reflected by the reflective liquid crystal display element without changing the polarization direction. That is, since the green light remains S-polarized light even after being reflected by the reflective liquid crystal display element 30G, it is reflected again by the polarization separation surface of the first polarization beam splitter 29 and passes through the incident-side polarizing plate 28. To return to the light source side. In general, since the S-polarized light has better detection performance than the P-polarized light, the projection optical system 37 is compared with the first embodiment that employs a configuration in which green light having high visibility is incident on the liquid crystal display element as the P-polarized light. Green light leaks less. That is, there is a feature that it is easy to increase the contrast.

(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. Parts not specifically described are the same as those in the first embodiment.

  The light source 1, the reflector 2, the illumination optical system 100, and the polarization conversion element (polarization conversion element array) (not shown) are the same as those in the first embodiment. Yes.

  The color separation / synthesis optical system 400 will be described with reference to FIG.

  The dichroic mirror 46 has characteristics of reflecting blue light (B) and red light (R) color light among white light from the light source and transmitting green light (G) color light.

  The optical path of green light that has passed through the dichroic mirror 46 will be described.

  Reference numeral 47 denotes a mirror that reflects the green light transmitted through the dichroic mirror 46. 48 is an incident-side polarizing plate that transmits only P-polarized light (desired polarization direction) and absorbs or reflects S-polarized light orthogonal to the P-polarized light (light having a polarization direction orthogonal to the desired polarization direction). (Incident side polarizing plate for green light, first incident side polarizing plate). Reference numeral 49 denotes a first polarization beam splitter having the polarization separation characteristic shown in FIG. 5, in which blue light is transmitted regardless of the polarization direction, green light and red light are transmitted through P-polarized light, and S-polarized light is reflected. A first polarizing beam splitter having a surface.

  Reference numeral 50G denotes a reflective liquid crystal display element for green (for green light) that reflects incident light and modulates an image, 51G is a quarter wavelength plate for green, and 70 is an optical path adjusting prism. The P-polarized green light that has passed through the first polarizing beam splitter 49 enters the reflective liquid crystal display element 50G for green light through the optical path adjusting prism 70 and the quarter wavelength plate 51G. The green light incident on the reflective liquid crystal display element is image-modulated (for example, partly modulated to S-polarized light) and reflected, and again passes through the quarter-wave plate 51G and the optical path adjusting prism 70, thereby being the first polarized beam. The light enters the splitter 49. Of the green light incident on the first polarization beam splitter, P-polarized light is transmitted through the polarization separation surface and guided to the light source direction, and S-polarized light is reflected by the polarization separation surface and guided to the projection optical system 56. In this way, the green image light is projected onto the projection surface by the projection optical system 56.

  The optical paths of blue light and red light reflected by the dichroic mirror 26 will be described.

  Red light and blue light are incident-side polarizing plates that transmit P-polarized light and absorb or reflect S-polarized light among red and blue light (incident-side polarizing plates for red light and blue light, or polarized light for white light). Plate, second incident side polarizing plate) 52. The red light and blue light that have passed through the incident-side polarizing plate 52 are incident on the wavelength-selective phase difference plate 53 as P-polarized light. This wavelength-selective retardation plate (color-selective retardation plate) 53 has a function of rotating only the polarization direction of red light by 90 degrees without changing the polarization direction of blue light (1/0 with respect to red light). Functions as a two-wave plate). Therefore, the blue light emitted from the wavelength selective phase difference plate 53 remains P-polarized light, but the red light is converted into S-polarized light.

  Reference numeral 54 denotes a second polarization beam splitter, which is a polarized light that transmits P-polarized light and reflects S-polarized light for both red light and blue light (for all color lights of red, green, and blue light). Has a separation surface. Accordingly, the P-polarized blue light (illumination light) is transmitted through the second polarization beam splitter 54 (the polarization separation surface thereof), passes through the quarter-wave plate 51B, and is reflected for blue (for blue light). Incident on element 50B. The blue light modulated and reflected by the blue reflective liquid crystal display element 50B is incident on the second polarizing beam splitter 54 again through the quarter-wave plate 51B. Of the blue light incident on the second polarizing beam splitter 54, blue light (image light) modulated into S-polarized light in the liquid crystal display element 50 </ b> B is reflected by the second polarizing beam splitter and is reflected by the projection optical system 56. Guided in the direction.

  The S-polarized red light (illumination light) incident on the second polarizing beam splitter 54 is reflected and passes through the quarter-wave plate 51R to the red (red light) reflective liquid crystal display element 50R. Incident. The red light modulated and reflected by the red reflective liquid crystal display element 50R enters the second polarizing beam splitter 54 again through the quarter-wave plate 51R. Of the red light incident on the second polarizing beam splitter 54, red light (image light) modulated into P-polarized light in the liquid crystal display element 50R passes through the second polarizing beam splitter and passes through the projection optical system 56. Guided in the direction.

  The P-polarized red light and the S-polarized blue light guided from the second polarizing beam splitter in the direction of the projection optical system 56 are incident on the blue light-dedicated polarizing plate (blue-dedicated emission-side polarizing plate) 55. To do. This blue light polarizing plate (outgoing side polarizing plate) 55 has the characteristics shown in FIG. 6, that is, it transmits S-polarized light for blue light and reflects or absorbs P-polarized light, and in the polarization direction for red light. Regardless of its transmission characteristics. Therefore, the P-polarized red light (image light) and the S-polarized blue light (image light) are transmitted through the blue light-dedicated polarizing plate 55, but if P-polarized blue light (unnecessary light) is mixed. Is reflected or absorbed by the blue light polarizing plate 55 so as not to enter the projection optical system.

  Next, P-polarized red light (image light) and S-polarized blue light (image light) are incident on the first polarization beam splitter 49. The first polarizing beam splitter 49 transmits (or may reflect) all of the blue light regardless of the polarization direction, and has a polarization separation surface that reflects S-polarized light and transmits P-polarized light for red light. Have. Therefore, if S-polarized red light is mixed, it is reflected by the first polarizing beam splitter and guided in a direction different from that of the projection optical system.

  As a result, P-polarized red light (image light) and S-polarized blue light (image light) are transmitted through the first polarization beam splitter, and S-polarized green light (image light) is transmitted through the first polarization beam splitter. The red, green, and blue light are combined and guided to the projection optical system 56.

  In the case of black display, each color light is returned to the light source direction as in the first embodiment.

  Also in the third embodiment, a lens may be disposed between the first polarizing beam splitter and the green reflective liquid crystal display element 50G. Further, between the first polarizing beam splitter and the second polarizing beam splitter, between the second polarizing beam splitter and the red reflective liquid crystal display element, or between the second polarizing beam splitter and the blue reflective liquid crystal. A lens may be disposed between the display element and the display element.

(Fourth embodiment)
In the first, second, and third embodiments, one white light source (a light source that emits white light, a light source that emits all of red, green, and blue light) is used. However, the present invention is not limited thereto. Alternatively, a plurality of light sources may be used. In the fourth embodiment, a light source for green light (first color light), blue light and red light (second and third color lights) may be provided. ) For example (a configuration having two light sources). Example 4 will be described with reference to FIG.

  First, 61 in FIG. 7 is a light source (first light source) for green light (first color light, for light in the first wavelength region), and 62 is for blue light and red light (second, third, light). This is a light source (second light source) for color light, for light in the second and third wavelength regions, and for second and third liquid crystal display elements.

  The light source for green light (first light source) 61 and the light source for blue light and red light (second light source) 62 are each composed of a plurality of LEDs.

  The green light emitted from the green light source 61 passes through the incident-side polarizing plate 8 (first incident-side polarizing plate) that transmits the P-polarized light and absorbs or reflects the S-polarized light as in the first embodiment. The light enters the beam splitter 9. Accordingly, substantially only P-polarized green light is incident on the first polarization beam splitter 9.

  Blue and red light from the light source 62 for blue light and blue light are incident on an incident side polarizing plate (second incident side polarizing plate) 12 that transmits P-polarized light and absorbs or reflects S-polarized light as in the first embodiment. Thus, the degree of polarization can be increased (the ratio of a desired polarization component is improved). The blue light and red light that have passed through the incident-side polarizing plate enter the second polarizing beam splitter 13 (a polarizing beam splitter having polarization separation characteristics as shown in FIG. 2). Accordingly, substantially only P-polarized blue light and P-polarized red light are incident on the second polarizing beam splitter 13.

  After entering the first polarizing beam splitter and the second polarizing beam splitter, the optical action is the same as that of the first embodiment, and thus the description thereof is omitted.

  In the fourth embodiment, a light source composed of a plurality of LEDs is used. However, the present invention is not limited to this, and a laser light source or the like may be used. Further, a combination of a white light source (such as a high-pressure mercury lamp) and a color filter may be used instead of the light source of this embodiment.

  The first, second, third, and fourth embodiments described above may be arbitrarily combined. For example, the optical path adjusting prism 70 described in the second, third, and fourth embodiments may not be disposed as shown in FIGS. 8 and 9, or may be replaced with a lens or the like. Further, in the arrangement as in the second embodiment, a wavelength selective phase difference plate may be used as in the third embodiment.

Schematic diagram of the first embodiment. Explanatory drawing of the polarization separation characteristic of the 2nd polarizing beam splitter 13 of 1st Example. Schematic diagram of the second embodiment. Schematic diagram of the third embodiment. Explanatory drawing of the polarization separation characteristic of the 1st polarizing beam splitter 49 in 3rd Example. Explanatory drawing of the characteristic of the polarizing plate 55 only for blue light in 3rd Example. Schematic diagram of the fourth embodiment. Schematic of the 1st modification of 1st Example. Schematic of the 2nd modification of 1st Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Reflector 3 1st lens array 4 2nd lens array 5 Condenser lens 6, 26, 46 Dichroic mirror 7, 27, 32, 47 Mirror 8, 12, 28, 33, 48, 52 Incident side polarizing plate 9 , 29, 49 First polarizing beam splitter 10, 30, 50 Reflective liquid crystal display element 11, 31, 51 1/4 wave plate 13, 34, 54 Second polarizing beam splitter 14, 35 Emission side polarizing plate 15, 36 1/2 wavelength plate 53 Wavelength selective phase difference plate 55 Polarizing plate for blue light 16, 37, 56 Projection optical system (projection lens)
61 Light source for green light 62 Light source for blue light and red light 100 Illumination optical system 200, 300, 400 Color separation / synthesis optical system

Claims (9)

A first polarization separation surface having polarization separation characteristics for light in the first wavelength region;
A color separation / synthesis optical system comprising a second polarization separation surface having polarization separation characteristics for light in the second and third wavelength regions,
The first polarization separation surface guides the illumination light in the first wavelength region to the first liquid crystal display element, and guides the image light reflected by the first liquid crystal display element in a direction different from the illumination light. ,
The second polarization separation surface decomposes the illumination light in the second wavelength region and the illumination light in the third wavelength region and guides them to the second liquid crystal display element and the third liquid crystal display element, respectively, and the second liquid crystal The image light reflected by the display element and the image light reflected by the third liquid crystal display element are combined and guided to the first polarization separation surface;
The first polarization separation surface combines the image light reflected by the first liquid crystal display element and the image light reflected by the second and third liquid crystal display elements synthesized by the second polarization separation surface. A color separation / synthesis optical system. A first incident-side polarizing plate disposed on the light source side of the first polarization separation surface and functioning as a polarizing plate for the light in the first wavelength region;
A second incident-side polarizing plate disposed on the light source side of the second polarization separation surface and functioning as a polarizing plate for the light in the second wavelength region and the light in the third wavelength region, The color separation / synthesis optical system according to claim 1.   An output-side polarizing plate that functions as a polarizing plate for light in at least one of the second wavelength region and the third wavelength region between the first polarization separation surface and the second polarization separation surface. The color separation / synthesis optical system according to claim 1, further comprising:   The second polarization separation surface transmits S-polarized light and reflects P-polarized light for light in the second wavelength region, and reflects S-polarized light for light in the third wavelength region. 4. The color separation / synthesis optical system according to claim 1, wherein the color separation / synthesis optical system has a characteristic of transmitting P-polarized light. The first polarization separation surface transmits the first linearly polarized light with respect to all the light in the first, second and third wavelength regions, and the second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light. It has the property of reflecting light,
The color separation / synthesis optical system according to claim 1, further comprising a half-wave plate between the first polarization separation surface and the second polarization separation surface.   The polarization direction of light in the first wavelength region incident on the first polarization separation surface, the polarization direction of light in the second wavelength region incident on the second polarization separation surface, and incident on the second polarization separation surface 6. The color separation / synthesis optical system according to claim 1, wherein the polarization direction of the light in the third wavelength region is the same. The polarization direction of the light in the second wavelength region incident on the second polarization separation surface is orthogonal to the polarization direction of the light in the third wavelength region,
The second polarization separation surface transmits the first linearly polarized light with respect to the light in the second wavelength region and the light in the third wavelength region, and a second direction in which the polarization direction is orthogonal to the first linearly polarized light. It has the property of reflecting linearly polarized light,
A polarizing plate that functions as a polarizing plate between the first polarized light separating surface and the second polarized light separating surface as a polarizing plate for the light in the second wavelength region, and transmits all the light in the third wavelength region. With
The first polarization separation surface has a polarization separation function for the light in the first wavelength region and the light in the third wavelength region, and reflects or transmits all the light in the second wavelength region. The color separation / synthesis optical system according to claim 1, wherein the color separation / synthesis optical system has characteristics. First, second and third liquid crystal display elements;
A projection optical system that projects image light from the first, second, and third liquid crystal display elements;
Image projection comprising: a color separation / synthesis optical system that guides light from a light source to the first, second, and third liquid crystal display elements and guides image light from the first, second, and third liquid crystal display elements to the projection optical system A device,
The color separation / synthesis optical system comprises:
A first polarization separation surface having polarization separation characteristics for light in the first wavelength region;
A second polarization separation surface having polarization separation characteristics for light in the second and third wavelength regions,
The first polarization separation surface guides the illumination light in the first wavelength region to the first liquid crystal display element, and guides the image light reflected by the first liquid crystal display element to the projection optical system,
The second polarization separation surface decomposes the illumination light in the second wavelength region and the illumination light in the third wavelength region and guides them to the second liquid crystal display element and the third liquid crystal display element, respectively, and the second liquid crystal The image light reflected by the display element and the image light reflected by the third liquid crystal display element are combined and guided to the first polarization separation surface;
The first polarization separation surface combines the image light reflected by the first liquid crystal display element and the image light reflected by the second and third liquid crystal display elements synthesized by the second polarization separation surface. Then, the image projection apparatus is guided to the projection optical system. A first light source that emits light in the first wavelength region; and a second light source that emits light in the second and third wavelength regions;
Illuminating the first liquid crystal display element with illumination light from the first light source;
The image projection apparatus according to claim 8, wherein the second and third liquid crystal display elements are illuminated with illumination light from the second light source.

Images